In the textile industry, textile fibres are assembled mechanically during at least one mechanical assembly stage such as spinning (all the operations for assembling fibres together in order to obtain a thread); braiding, knitting and weaving (assembling threads by interlacing and/or looping together etc.); felting, adhesive bonding, agglomeration of fibres and/or threads and/or several materials to each other or to other products (non-woven, composite etc.)
After these assembly stages, the so-called "loomstate" or gray pieces, undergo finishing treatments (desizing, bleaching, dyeing, printing, application of finishes, etc.).
At the end of all these stages, the textile structure obtained has the desired forms and appearance, but it incorporates many undesirable and useless impurities, trapped within the structure, and which do not enter into the composition of the fibres or the structure. Among these impurities reference may be made to: impurities incorporated in the fibres when the fibres themselves are obtained or manufactured; additives and impurities deliberately incorporated or not (for example oiling or antistatic additives) during the assembly stages; organic contaminants or microorganisms etc.
Taking into account the great difficulty of eliminating all these impurities incorporated within the structure itself and the fibres, one is resigned in most applications to use these textile structures contaminated in this way.
In the particular case where purification is essential, for example for the manufacture of implantable materials having a textile fibre structure (artificial ligaments, adhesive dressings, artificial membranes, vascular prostheses etc) a succession of multiple complex stages are carried out having very different natures(suitable for eliminating each type of impurity) which are sophisticated : washing, cleaning desizing, disinfecting, elimination of solvents, neutralization etc.
All these treatments consist of using active products such as detergents, disinfectants and harmful powerful solvents which may themselves remain as traces in the structure and are dangerous for operators. Moreover, these treatments are long, costly and often polluting as a result of the use of these powerful and harmful products.
In spite of all these treatments, it is not a rare occurrence to find that the structures remain somewhat contaminated. For example, it has been demonstrated that negative immune reactions may be due to these types of contamination on the surface of vascular prosthesis implanted under perfectly sterile conditions.
Such is in particular the case with structures of bioresorbable textile fibres made of sensitive polymers which do not withstand solvents, detergents or disinfectants, or heat treatments. The use of these fibres for the manufacture of parts requiring great purity has therefore hitherto been rejected.
Now, these delicate textile fibres sometimes possess, moreover, particular properties which are desired for precise applications. Such is the case in particular of fibres containing at least one poly(.alpha.-hydroxy-acid) which are biocompatible and/or biodegradeable, and in particular fibres of polyglycollic acid (PGA) which have excellent bioresorption properties.
Nevertheless, it was hitherto considered that polymers of the poly(.alpha.-hydroxy-acids) family could not be subjected to intense physico-chemical treatments, taking into account their great fragility. In particular, it is known that polymers of the poly(.alpha.-hydroxy-acids) family are soluble in fluids in the supercritical state (cf. for example "Formation of bioredible polymeric microspheres and microparticles by rapid expansion of supercritical solutions", J. W. Tom and P. G. Debenedetti, Biotechnol. Prog., 1991, 7, 403-411; EP-0 464 163 etc). Moreover purification treatments applied to these materials have the consequence of making them fragile, even though these treatments always remain imperfect. Thus for many applications, the need has been apparent for a treatment process enabling textile structures based on polymers of the poly(.alpha.-hydroxy-acids) family to be completely purified and which does not degrade the mechanical properties of the structure.